Radiocarbon ages and tsunami deposits in laminated mud layers from the Lake Harutori, Pacific coast of Hokkaido, Northeast Japan

To identify temporal changes in the marine reservoir effect in Northeast Japan, the radiocarbon ages of terrestrial plants and marine shells were measured from two cores obtained from Lake Harutori in Kushiro City. This lake located where one of the highest marine reservoir effect was detected in East Asia, facing the Oyashio cold current. This drilling site is situated in a tectonically active region of the southwestern Kuril arc. Based on lithological analyses, molluscan assemblages, and radiocarbon dating, we interpreted five units in order of decreasing age: basement coastal sediments, estuary sediment, laminated sediment, inner bay sediment, and artificial fills. These sediments consisted of laminated mud beds with terrestrial plant fragments and intercalating tsunami sand beds. The structure was imaged using core scanning computed tomography and X-ray fluorescence. The reservoir ages of seven pairs were obtained from estuary sediment to inner-bay sediment over the past 9000 years.